The invention relates to a method for detecting defects in sheet metal segments of electric generators and electric motors, wherein between the sheet metal pieces of the sheet metal segments an electric insulating layer is arranged, respectively, and wherein between the sheet metal segments cooling channels are provided. The detection method comprises generating magnetic induction in the sheet metal segments by applying externally a magnetic field and measuring the temperature of the heat generated in the sheet metal segment. The invention further relates to a device for performing the method.
The present invention is designed for electric generators as well as electric motors for industrial applications. Such electric generators as well as electric motors are comprised of sheet metal segments of stacked sheet metal pieces. Thin electric insulation layers are arranged between the individual pairs of sheet metal pieces. The problem of these electric generators and motors resides in that, for example, as a result of aging or vibrations, loosening can occur, in particular, loosening of the windings within the package of sheet metal pieces, on the one hand, and loosening of the sheet metal pieces, on the other hand. The result of loosening of the sheet metal pieces is that the interposed insulation layers are subjected to wear. Because of this, short circuits can result which lead to heat generation and can cause core burning in extreme situations.
For detecting defects in the sheet metal segments with regard to possibly present wear of the insulators, it is known to apply an external magnetic field by means of a testing coil for high induction testing and to generate in this way magnetic induction within the sheet metal segment. In accordance with the level of wear, heat is generated within the sheet metal segment. This generated heat can be made visible by means of a thermocamera.
A disadvantage of this known method is that by means of a thermocamera only the surface of the sheet metal segments can be sensed with regard to the heat profile. A more precise information regarding the temperature in the interior of the sheet metal segment cannot be obtained in this way.